Analgesia efficacy of erector spinae plane block in laparoscopic abdominal surgeries: a systemic review and meta-analysis

Background: Multimodal analgesia is now widely practised to minimise postoperative opioid consumption while optimising pain control. The aim of this meta-analysis was to assess the analgesic efficacy of erector spinae plane block (ESPB) in patients undergoing laparoscopic abdominal surgeries. This will be determined by perioperative opioid consumption, subjective pain scores, and incidences of postoperative nausea and vomiting. Methods: The authors systemically searched electronic databases for randomised controlled trials (RCTs) published up to February 2023 comparing ESPB with other adjuvant analgesic techniques in laparoscopic abdominal surgeries. Nine randomised controlled trials encompassing 666 subjects were included in our study. Results: ESPB was shown to reduce postoperative opioid consumption [mean difference (MD) of −5.95 mg (95% CI: −8.86 to −3.04; P<0.0001); I2=89%], intraoperative opioid consumption MD of −102.4 mcg (95% CI: −145.58 to −59.21; P<0.00001); I2=39%, and incidence of nausea [RR 0.38 (95% CI: 0.25–0.60; P<0.0001); I2=0%] and vomiting [RR 0.32 (95% CI: 0.17–0.63; P=0.0009); I2=0%] in laparoscopic abdominal surgeries. Subgroup analysis on laparoscopic colorectal surgeries further showed reduction in postoperative pain scores MD of −0.68 (95% CI: −0.94 to −0.41); P<0.00001; I2=0%]. Conclusions: This study concludes that ESPB is a valuable technique with proven efficacy to potentially promote faster postoperative recovery through optimising pain control while minimising opioid requirements.


Introduction
Enhanced Recovery after Surgery (ERAS) protocols are rapidly becoming the standard of care for patients undergoing elective surgery with aims to expedite postoperative recovery and decrease morbidity with multimodal analgesia [1] .This encompasses not only oral analgesics like NSAIDS and opioids but also patient-controlled analgesia (PCA), and locoregional anaesthetic techniques such as epidural analgesia or interfascial plane blocks [1] .
Interfascial plane blocks (IPB) first came into the limelight with the introduction of the transversus abdominis plane block (TAPB) technique in 2001.This inspired a flurry of practisechanging research, giving rise to other variations such as the subcostal TAP, pectoralis, transversalis fascia, and erector spinae plane block (ESPB) among others.
ESPB was first demonstrated by Forero et al. [2] in 2016 in two case studies to primarily address thoracic neuropathic

HIGHLIGHTS
• Erector spinae plane block (ESPB) stands out due to its relative simplicity in comparison to other interfascial plane blocks.• ESPB reduced perioperative opioid consumption after laparoscopic abdominal surgeries thus contributing to the goals of enhanced recovery after surgery.• Reduction of opioid consumption with the use of ESPB reduces incidences of postoperative complications such as nausea and vomiting.• ESPB is an effective tool in the postoperative analgesic armamentarium.
pain in metastatic and malunion of rib fractures.Many other studies have since been performed to evaluate its analgesic efficacy in abdominal [3][4][5] and thoracic [6,7] surgeries.ESPB aims to provide both somatic and visceral analgesia although its mechanism of action has yet to be fully elucidated [8] .MRI studies proposed that infiltration of anaesthetic medications into the plane beneath the erector spinae results in both transforaminal and epidural spread.A block at the foramen where the thoracolumbar splanchnic nerves emerge results in visceral pathway blockade while epidural spread facilitates segmental blockade, addressing somatic pain [9] .The erector spinae muscle extends within the paravertebral groove on either sides of the vertebrae column, running from the skull to sacrum while being encased within a single aponeurosis.As such, local anaesthetic agents injected into this sub-fascial plane can spread in a cranio-caudal manner.Cadaveric studies have documented the extent of spread to be about three to four levels cranially and caudally [10] .When injected at the lower thoracic region, ESPB affects the lower thoracic nerve roots supplying the abdomen and hence, can potentially be used to provide analgesia for abdominal surgeries.ESPB stands out amongst other neuroaxial blocks because of its relative simplicity, ability to effectively provide both somatic and visceral analgesia to a wide area of the abdomen with a single level injection and optimal safety profile.The sonoanatomy of ESPB is easy to recognise and the anaesthetic agent is infiltrated within a plane far from crucial structures such as the pleura, vessels and medulla [11] .This is unlike the other blocks such as the thoracic paravertebral plane block (TPVB), which can reliably achieve both visceral and somatic [12] analgesia, but the benefits must be weighed against its relative complexity and complications such as pneumothorax [13] .In the case of epidural analgesia, its implementation has been associated with increased hemodynamic instability due to the sympatholytic effect of neuraxial blockade [14] .Transient detrusor muscle dysfunction caused by epidurals also necessitate the use of indwelling bladder catheters which increases the risk of catheter-associated urinary tract infection (CAUTI) [15] .
Despite its benefits, widespread adoption of ESPB has yet to gain significant traction.
This study aims to systematically review the literature reporting the efficacy of the ESPB as an adjuvant analgesia in laparoscopic surgeries.The primary outcome measure would be postoperative opioid consumption.Secondary outcomes are: intraoperative opioid consumption, postoperative pain scores and incidences of nausea and vomiting.

Literature review and search strategy
This review was conducted in line with the PRISMA [16] (Preferred Reporting Items for Systemic Reviews and Meta-Analysis) and AMSTAR [17] (Assessing the methodological quality of systemic review) guidelines.The scope of the review included randomised controlled trials (RCT) reporting the use of ESPB in laparoscopic abdominal surgeries in adults.Embase, PubMed, Scopus, and Google Scholar were searched up to February 2023.The search strategy and analytic plan of this systematic review and meta-analysis has been registered on PROSPERO.Procedures such as laparoscopic appendicectomy, cholecystectomy [18] , and ovarian cystectomies are now increasingly performed as day or short stay unit procedures.Postoperative pain can routinely be well controlled with regular NSAIDs, Paracetamol, and opioid as rescue analgesia.Hence, the use of interfascial plane blocks in patients undergoing these subset of procedures may not be indicated especially since the length of stay is often less than 24 h.

Type of outcome measures
We calculated postoperative opioid consumptions in terms of morphine (mg) using opioid dose conversions: 10 mg of morphine was equivalent to 0.01 mg Sufatenil and 0.1 mg Fentanyl [19] .Secondary outcomes were: intraoperative opioid consumption measured in intravenous fentanyl equivalents (mcg), pain scores quantified by the Visual Analogue Scale (VAS), and incidences of postoperative nausea and vomiting.Four RCTs utilised the Numerical Rating Scale (NRS) to quantify postoperative pain; however, data was not provided within the manuscript to allow for reliable analysis.NRS was therefore not evaluated as a secondary outcome.

Data extraction and quality assessment
The data was collected in accordance to the above inclusion and exclusion criteria.The search terms included a combination of 'erector spinae plane block', 'ESP block', 'ESPB', 'Laparoscopy', 'Laparoscopic', 'abdominal surgery', 'randomised controlled trial'.In papers with limited access, the respective authors were contacted and excluded if the request was unanswered.Quality of the studies was evaluated using the Cochrane Risk of Bias Tool.The risk of bias was graded accordingly into three levels (low risk, unclear risk, and high risk) as seen in Figure 1A.

Statistical analysis
The continuous variables were expressed as means SD and categorical variables were presented as proportions.For categorical outcomes, the risk ratio (RR) with 95% CI were calculated.For continuous outcomes, mean difference (MD) with 95% CI were calculated.If median [interquartile range, IQR] data was reported, it was converted into means SD by adopting the method of Hozo et al. [20] .Statistical heterogeneity was estimated by I 2 where I 2 of > 50% is considered significant heterogeneity and the random-effects model would be used.P-value < 0.05 was considered statistically significant.Sensitivity analysis was performed using bootstrapping approach to evaluate whether the results were influenced significantly by a single study.Data analysis were carried out using the Review Manager, Version 5.4.1 while sensitivity analysis was performed using Comprehensive Meta-Analysis, CMA Version 4.

Results of literature search
Our study selection process is shown in the PRISMA flow diagram (Fig. 1B).The literature search initially retrieved 1539 citations (Google Scholar 1000, PubMed 51, EmBase 449, Scopus 39).Of which, 34 relevant articles were identified through abstract screening.Nine studies with 666 participants were eventually included in the meta-analysis.

Patient characteristics and block techniques
Patient characteristics and block techniques are summarised in Table 1.There was no significant difference in baseline characteristic between the ESPB and Non-EPSB groups (which consisted of sham block, no block, intrathecal morphine, TAPB).The ESPB block is performed via ultrasound guidance at various thoracic levels predetermined by the anaesthesiologist involved in the studies.All studies used single shot ropivacaine or bupivacaine at differing concentrations (Min-Max: Ropivacaine 0.25-0.5%,Bupivacaine 0.125-0.25%).

Sensitivity analysis
Sensitivity analysis performed using bootstrapping method confirm that the findings were not significantly influenced by any single study (Supporting Information Table 1, Supplemental Digital Content 1, http://links.lww.com/JS9/C322).

Discussion
No previous study has attempted to assess ESPB in patients undergoing laparoscopic abdominal surgeries as previous studies often included open surgeries, laparotomy and day surgery procedures such as laparoscopic cholecystectomy [3,30] .These are excluded from our analysis which aims to evaluate the use of ESPB in the setting of major laparoscopic abdominal surgeries only.Herein, we focused on the analgesic efficacy of ESPB as compared to other analgesic modalities in this specific population of patients.This meta-analysis demonstrated that in patients undergoing laparoscopic abdominal surgery such as laparoscopic colorectal or bariatric surgery, the use of ESPB may benefit recovery in terms of reducing perioperative opioid consumption, and incidences of nausea and vomiting.There is; however, no significant difference in the postoperative pain scores when all surgeries were analysed together.Nonetheless, it is worth taking into consideration that while the VAS attempts to objectify pain which is a subjective experience, it is still vulnerable to inter and intraindividual variability [31] .This may be attributed to concomitant physical, physiological, and psychosocial factors that can confound the actual experience of 'pain'.Reassuringly, subgroup analysis focusing on laparoscopic colorectal surgeries showed that ESPB significantly reduced perioperative opioid requirements while achieving lower postoperative pain scores thus satisfying currentday ERAS recommendations and achieves its intended outcomes.
Therefore, it is reasonable that an effective regional block technique such as the ESPB be incorporated as a standard component of multimodal analgesia for laparoscopic abdominal surgeries.
IPB first came into the picture when Rafi [32] introduced the TAPB technique in 2001 with the aims of achieving a field block.
Advancements in ultrasound technology has allowed for TAPB to become widely employed as it was considered a safe and easy to perform therapeutic adjunct to pain control.However, TAPB can only reliably provide somatic analgesia to the anterior and/or lateral abdominal wall in postoperative patients, significantly limiting its efficacy.
Since its conceptualisation in 2016, ESPB has been unparalleled in terms of popularity in the field of regional anaesthesia.In fact, it has been recently included as one of the seven 'Plan A' blocks amongst other established techniques such as the interscalene block for shoulder surgery and the axillary block for upper limb surgery [33] .What sets ESPB apart is its versatility, ease of administration, and favourable safety profile.The ESPB can be performed at all levels of the spine to provide both somatic and visceral analgesia to various regions of the body.Rates of block failures are as low as less 8% when performed by both experienced and nonexperienced anaesthetists [34] because the sonoanatomy of ESPB is easy to learn, identify, and master.A survey of trainee anaesthetists found that of the seven Plan A blocks, there was a highest confidence level in administrating ESPB [35] .In terms of complications, ESPB is considered a superficial block with low risks for bleeding.In a review of 45 RCTs involving thoracic ESPB by De Cassai et al. [36] , there were no reported complications postprocedurally.In a head-on comparison between ESPB and TPVB which has been proven to be one of the most effective regional anaesthesia techniques for postoperative analgesia, ESPB was associated with significantly lower incidences of hemodynamic instability and block failures while offering noninferior analgesic effects [37] .In a similar study comparing ESPB to TPVB after modified radical mastectomy, four out of 35 patients that underwent TPVB developed pneumothorax while none in the ESPB group had similar presentations [38] .ESPB is a simple technique with superficial landmarks, unlike TPVB with close anatomic proximity to pleura and the central neuraxial system.
When pitted against epidural analgesia which has been considered the cornerstone of the ERAS programme especially in the setting of open colorectal surgery [39] , ESPB again demonstrated superiority with fewer procedural complications and noninferior analgesic efficacy [40] .ESPB can also be administered to patients who are coagulopathic or has received recent anticoagulation as it targets the myofascial plane far away from the neuraxial system [41] .Furthermore, epidural analgesia itself has not demonstrated similar success in the setting of laparoscopic abdominal surgeries.A previous meta-analysis performed by Giuseppe et al., which looked at five RCTs involving 163 patients found that epidural was in fact associated with a significantly increased duration of stay, without any significant difference in postoperative complications and readmissions as compared to other analgesic techniques [42] .In addition, combining epidural and general anaesthesia may lead to more profound hypotension due to sympathetic blockade and by extension, increase the risk of anastomotic breakdown due to compromised blood supply and oxygen delivery to peripheral tissues during episodes of hypotension.Notwithstanding the hemodynamic implications of epidural analgesia, the placement of epidural catheters in itself may also be challenging with failure rates ranging from 13 to 32% [43] .
This pooled analysis validates the efficacy of ESPB as an adjuvant analgesia in laparoscopic surgeries.Along with its favourable side effect profile and ease of administration, ESPB proves itself to be a promising adjunct for multimodal analgesia.
Nonetheless while ESPB may show significant promise, it is prudent for practitioners to recognise early symptoms of Local Anaesthesia Systemic Toxicity (LAST).Like other interfascial plane blocks, ESPB are regarded as 'volume' blocks [44] and local anaesthetic agents are injected in large volumes into a highly vascularised plane [45] hence resulting in a significant risk of LAST.Studies [46] have suggested that ESPB may result in LAST even when anaesthetic agents not administered at their maximum doses.Possible contributing factors include age, comorbids, and concurrent drug use [47] .To mitigate this, Shigeta et al. [48] recommended the use of adjunctive epinephrine with local anaesthetics in patients with increased risk of LAST as epinephrine reduces the rate at which local anaesthetic agents diffuse into the plasma, delays systemic uptake, and decreases the toxic effect on vulnerable tissues, such as the myocardium and central nervous system (CNS).Yawata et al. [49] also suggested that levobupivacaine could be associated with a higher risk of LAST in comparison to other agents such as ropivacaine.However, due to the relatively low incidence of LAST, further studies are needed to elucidate its risk factors and ways to reduce its occurrence.This study is limited in terms of the number of available studies and high between-study heterogeneity which could impact the robustness of our findings.Due to the limited number of studies, subgroup analysis could not be performed to identify potential heterogeneity or compare ESPB in upper and lower abdominal surgeries which could potentially yield different pain experiences.While the various studies have ensured administration of anaesthetic agents into the erector spinae plane with the use of ultrasound guidance, there is unfortunately a lack of standardisation of the thoracic level as well as the concentration and volume of anaesthetic agents used.In addition, we recognise that the included studies had utilised two distinct pain assessment tools -VAS and NRS.Data on NRS was not included in our analysis as several RCTs employed a graphical representation of NRS and extrapolation of such data could compromise its reliability.Moreover, despite similarities between NRS and VAS, they are not parallel scores and direct conversions should not be made.As such, only VAS was analysed in our study.Lastly, other secondary outcomes such as time to bowel movement or length of hospital stay were not evaluated.
In conclusion, ESPB is a promising regional anaesthetic technique for perioperative analgesia after laparoscopic abdominal surgeries.Nonetheless, due to high levels of heterogeneity, larger samples, and high quality RCTs are required to further strengthen and verify our results.

Figure 1 .
Figure 1. A. Risk of bias assessment of included studies.B. PRISMA flowchart of included and excluded studies.

Figure 2 .
Figure 2. Forest plot of (A) 24 hour cumulative postoperative intravenous morphine consumption in mg (B) intraoperative intravenous fentanyl consumption in mcg (C) pain score at 24 h postoperatively (D) incidence of postoperative nausea in first 24 h (E) incidence of postoperative vomiting in first 24 h; ESPB: erector spinae plane block, df: degree of freedom.

Figure 3 .
Figure 3. Subgroup analysis of laparoscopic colorectal procedures (A) 24 h cumulative postoperative intravenous morphine equivalent consumption in mg (B) intraoperative intravenous fentanyl equivalent consumption in mcg (C) 24 h postoperative pain scores; ESPB: erector spinae plane block, df: degree of freedom.

Table 1
Patient characteristics and block techniques employed in the included studies.